The present invention relates to a method of manufacturing a multi electron source serving as an electron source having many electron-emitting devices, a method of manufacturing an image forming apparatus using the multi electron source, an apparatus for manufacturing the multi electron source, and a method of adjusting the multi electron source.
Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter), and surface-conduction type electron-emitting devices.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
A known example of the MIM type electron-emitting devices is described in C. A. Mead, xe2x80x9cOperation of tunnel-emission devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961).
A known example of the surface-conduction type electron-emitting devices is described in, e.g., M. I. Elinson, xe2x80x9cRadio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction type electron-emitting device utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], a carbon thin film [Hisashi Araki et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 67 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction type electron-emitting devices. In FIG. 67, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 67. An electron-emitting portion 3005 is formed by performing electrification processing (to be referred to as forming processing) with respect to the conductive thin film 3004. An interval L in FIG. 67 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction type electron-emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In forming processing, for example, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied to the two ends of the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after forming processing, electrons are emitted near the fissure.
As described above, the electron-emitting portion of the surface-conduction type electron-emitting device is formed by processing (forming processing) of flowing a current through a conductive thin film to partially destroy or deform this thin film, thereby forming a fissure. If activation processing is performed subsequently, electron-emitting characteristics can be greatly improved.
In activation processing, the electron-emitting portion formed by forming processing is electrified under appropriate conditions to deposit carbon or a carbon compound around the electron-emitting portion. For example, graphite monocrystalline, graphite polycrystalline, amorphous carbon, or mixture thereof is deposited to a thickness of 500 xc3x85 or less around the electron-emitting portion by periodically applying a voltage pulse in a vacuum atmosphere in which an organic substance exists at a proper partial pressure and the total pressure is 10xe2x88x922 to 10xe2x88x923 Pa. These conditions are merely an example and properly changed in accordance with the material and shape of the surface-conduction type electron-emitting device.
This processing can increase the emission current at the same application voltage typically 100 times or greater the emission current immediately after forming processing. Note that the partial pressure of the organic substance in the vacuum atmosphere is desirably reduced after activation processing. This is called stabilization processing.
The above surface-conduction type electron-emitting devices are advantageous because they have a simple structure and can be easily manufactured. For this reason, many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of surface-conduction type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, electron sources, and the like have been studied.
As an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open No. 2-257551 filed by the present applicant, an image display apparatus using a combination of a surface-conduction type electron-emitting device and a fluorescent substance which emits light upon reception of electrons has been studied. This type of image display apparatus using a combination of the surface-conduction type electron-emitting device and the fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, the above display apparatus is superior to recent popular liquid crystal display apparatuses in that it does not require a backlight because of a self-emission type and has a wide view angle.
The present inventors have examined surface conduction type electron-emitting devices of various materials, various manufacturing methods, and various structures, in addition to the above-mentioned conventional surface conduction type electron-emitting device. Further, the present inventors have made extensive studies on a multi-beam electron source having a large number of surface-conduction type electron-emitting devices, and an image display apparatus using this multi-beam electron source.
The present inventors have examined a multi electron source using an electrical wiring method shown in, e.g., FIG. 68. That is, a large number of surface-conduction type electron-emitting devices are two-dimensionally arranged in a matrix to obtain a multi electron source, as shown in FIG. 68.
In FIG. 68, reference numeral 4001 denotes a surface-conduction type electron-emitting device; 4002, a row-direction wiring; and 4003, a column-direction wiring. The row- and column-direction wirings 4002 and 4003 actually have finite electrical resistances, which are represented as wiring resistances 4004 and 4005 in FIG. 68. This wiring method is called a simple matrix wiring method.
For the illustrative convenience, the multi electron source is illustrated in a 6xc3x976 matrix, but the size of the matrix is not limited to this. For example, in a multi electron source for an image display apparatus, a number of devices enough to display a desired image are arranged and wired.
In a multi electron source in which surface-conduction type electron-emitting devices are arranged in a simple matrix, appropriate electrical signals are applied to the row- and column-direction wirings 4002 and 4003 in order to output a desired electron beam. For example, to drive surface-conduction type electron-emitting devices on an arbitrary row in the matrix, a selection voltage Vs is applied to the row-direction wiring 4002 on the row to be selected, and at the same time a non-selection voltage Vns is applied to the row-direction wirings 4002 on unselected rows. In synchronism with this, a driving voltage Ve for emitting an electron beam is applied to the column-direction wirings 4003. According to this method, so long as voltage drops across the wiring resistances 4004 and 4005 are neglected, a voltage (Vexe2x88x92Vs) is applied to the surface-conduction type electron-emitting device on the selected row, and a voltage (Vexe2x88x92Vns) is applied to the surface-conduction type electron-emitting devices on the unselected rows. When the voltages Ve, Vs, and Vns are set to appropriate levels, an electron beam having a desired intensity must be output from only surface-conduction type electron-emitting devices on a selected row. When different driving voltages Ve are applied to respective column-direction wirings, electrons having different intensities must be output from respective devices on a selected row. Since the surface-conduction type electron-emitting device has a high response speed, the electron beam output time can be changed by changing the application time of the driving voltage Ve.
A multi electron source obtained by arranging surface-conduction type electron-emitting devices in a simple matrix can be applied for a variety of purposes. For example, if a voltage signal corresponding to image information is appropriately applied, the multi electron source can be applied as an electron source for an image display apparatus.
The present inventors have made extensive studies on improving the characteristics of the surface-conduction type electron-emitting device to find that changes over time can be reduced by performing a step (to be referred to as pre-driving processing hereinafter) of applying a voltage which satisfies a specific relationship with a normal driving voltage before normal driving is executed for the surface-conduction type electron-emitting device.
The present applicants have proposed that changes in device characteristics upon actual driving can be suppressed by applying a voltage higher than a voltage applied in actual driving, as the manufacturing process of the surface-conduction type electron-emitting device.
It is an object of the present invention to provide a pre-driving apparatus and method and an electron source manufacturing method capable of applying pre-driving processing to an electron source having many electron-emitting devices arranged in a matrix or ladder shape on a substrate, shortening the process evaluation time, and giving uniform electron-emitting characteristics to electron-emitting devices constituting the electron source.
To achieve the above object, an electron source manufacturing method according to the first aspect of the present invention has the following steps.
That is, a method of manufacturing an electron source having a plurality of electron-emitting devices is characterized by comprising:
the voltage application step of applying potentials to each first wiring commonly connected to a plurality of devices, and a plurality of second wirings respectively connected to the plurality of devices, such that a voltage V1 is applied to the plurality of devices connected to the first wiring by the potentials applied to the first wiring and the plurality of second wirings, the voltage V1 having a relationship with a maximum value V2 of a voltage applied as a normal driving voltage after the voltage application step, so as to satisfy:
giving a current I flowing upon application of a voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between two electrodes is applied to the device:
I=f(V)xe2x80x83xe2x80x83(1)
and letting fxe2x80x2(V) be a differential coefficient of f(V) at the voltage V,
a condition:
f(V1)/{V1xc2x7fxe2x80x2(V1)xe2x88x922f(V1)} greater than f(V2)/{V2xc2x7fxe2x80x2(V2)xe2x88x922f(V2)}xe2x80x83xe2x80x83(2)
wherein the potential applied to the second wiring is set to reduce a difference in magnitude of the voltage V1 applied to each device as a potential difference between the potential applied to the device through the first wiring and the potential applied to the device through the second wiring. Particularly in this aspect, the difference between application voltages to devices caused by a voltage drop on the first wiring is preferably reduced by setting different potentials to the second wirings.
If devices are connected at a plurality of positions on the first wiring, the potential applied to these devices through the first wiring varies. At this time, if the same potential is applied to the devices through the second wirings, the voltage V1 applied to the devices greatly varies. To prevent this, the present invention sets the potentials applied to the second wirings so as to reduce the differences in magnitudes of the voltage V1 applied to the devices. Accordingly, an electron source can be suitably manufactured.
In the present invention, the voltage application step is preferably performed in a high vacuum atmosphere. The voltage application step is preferably performed in an atmosphere in which deposition of a substance in the atmosphere or a substance originating from the substance in the atmosphere is suppressed at a portion serving as an electron-emitting portion of each device. For example, the voltage application step is preferably performed in an atmosphere in which a substance serving as a deposit has a partial pressure of not more than 1xc3x9710xe2x88x926 Pa.
In the present invention, it is preferable that each device have two electrodes, the two electrodes sandwich a gap, and the voltage application step be performed in an atmosphere in which the gap between the two electrodes is not narrowed by deposition of a substance in the atmosphere or a substance originating from the substance in the atmosphere.
In the present invention, the voltage application step is preferably performed in an atmosphere in which carbon or a carbon compound in the atmosphere has a partial pressure of not more than 1xc3x9710xe2x88x926 Pa.
In the present invention, the voltage application step is preferably performed after the step of depositing a deposit at a portion serving as an electron-emitting portion of each device. For example, the deposit preferably contains carbon. The deposit may be a carbon compound
The manufacturing method of the present invention can be preferably adopted when the electron-emitting device is a cold cathode device. In particular, the manufacturing method can be preferably adopted when the electron-emitting device is a field emission type electron-emitting device, surface-conduction type electron-emitting device, or MIM type electron-emitting device having an insulating layer sandwiched between two electrodes.
As the manufacturing process of the surface-conduction type electron-emitting device, the activation step is known in which carbon or a carbon compound is deposited in a gap serving as an electron-emitting portion. The voltage application step of the present invention is suitable as a step performed after the activation step. The voltage application step of the present invention is preferably performed after the partial pressure of a substance serving as a deposit in the atmosphere is decreased upon the deposition step.
In the present invention, particularly, the potential applied to each second wiring is preferably updated during the voltage application step.
By updating the potential applied to the second wiring, a preferable voltage application state can be maintained in accordance with changes in device characteristics. The potential can be updated along with the progress of the voltage application step such that the application potential is changed every predetermined time. In particular, the potential can be preferably updated in accordance with a state detected by, e.g., detecting a current flowing through the wiring. Specifically, an appropriate potential can be supplied to the second wiring using a measurement circuit for measuring a current flowing through the device in the voltage application step, a calculation circuit for calculating a potential to be applied to the second wiring on the basis of an output from the measurement circuit, and a potential distribution generation circuit for setting a potential to be applied to the second wiring by the calculation circuit. Even if a current flowing through the device changes, a potential applied to the second wiring can be properly set in accordance with the change. More specifically, the potential distribution generation circuit can be constituted by a latch circuit holding the potential of each second wiring calculated by the calculation circuit, and a D/A converter for converting an output from the latch circuit into an analog value. A current flowing through the device can be detected directly or indirectly by detecting a current flowing through the wiring, as described above.
The current can be detected by a method of detecting a current flowing through the first wiring or a method of detecting a current flowing through each second wiring.
In the present invention, the voltage application step preferably comprises applying a pulse-like potential.
In the present invention, it is preferable that the voltage application step comprises applying a pulse-like voltage to each device a plurality of number of times. The pulse-like voltage is applied by applying as pulses at least one of the potential applied to the first wiring and the potential applied to the second wiring. For example, when the potential of the first wiring is in a predetermined state, a pulse-like potential is applied to the second wiring, thereby applying a pulse-like voltage to the device. While the potential of the first wiring is in a predetermined state, a pulse-like potential is applied through the second wiring a plurality of number of times, thereby applying a pulse-like voltage a plurality of number of times. Alternatively, the step of applying a predetermined potential to the first wiring may be repeated a plurality of number of times, thereby providing a chance to apply a pulse-like voltage to the device a plurality of number of times.
In the present invention, the potential applied to the first wiring is set to distribute the potentials applied to the plurality of second wirings with respect to a potential of 0 V.
In the present invention, the voltage application step includes the step of selecting some of a plurality of first wirings, and a predetermined potential is applied to the selected first wirings to apply the voltage V1 to a plurality of devices connected to the selected first wirings.
At this time, a predetermined potential different from the potential applied to the selected first wirings is preferably applied to first wirings other than the selected first wirings. In particular, the potential is preferably applied to the unselected first wiring so as to suppress a current flowing through a device which receives a potential through the unselected first wiring.
In the present invention, the predetermined potential different from the potential applied to the selected first wirings is preferably a potential smaller than a maximum value and larger than a minimum value among the potentials applied to the plurality of second wirings in order to apply the voltage V1 to a plurality of devices connected to the selected first wirings.
The voltage application step comprises applying the voltage V1 to a plurality of devices connected to each first wiring while sequentially changing the first wirings to be selected.
First wirings to be simultaneously selected in the voltage application step are some of the plurality of first wirings.
The method preferably further comprises the step of determining first wirings to be simultaneously selected.
The step of determining first wirings to be simultaneously selected comprises determining the number of-first wirings to be simultaneously selected, or selecting first wirings to be simultaneously selected. The step of determining first wirings to be simultaneously selected can be executed during the voltage application step. More specifically, first wirings to be simultaneously selected can be determined based on the wiring resistance value or a detected current value. Alternatively, first wirings to be simultaneously selected may be determined by storing, in a memory, information for determining first wirings to be simultaneously selected, and referring to the information.
In the present invention, it is preferable that first wirings to be simultaneously selected in the voltage application step be some of the plurality of first wirings, and the method further comprises the step of determining unselected first wirings from the plurality of first wirings.
An electron source manufacturing method according to the second aspect of the present invention includes the following steps.
That is, a method of manufacturing an electron source having a plurality of electron-emitting devices respectively connected to a plurality of first wirings, is characterized by comprising:
the voltage application step of selecting some first wirings from the plurality of first wirings, and applying a voltage V1 to a plurality of devices connected to each of the selected first wirings by potentials applied to the selected first wirings and a potential applied to a second wiring connected to the plurality of devices respectively connected to the selected first wirings, the voltage V1 having a relationship with a maximum value V2 of a voltage applied as a normal driving voltage after the voltage application step, so as to satisfy:
giving a current I flowing upon application of the voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between two electrodes each device is applied to the device:
I=f(V)xe2x80x83xe2x80x83(1)
and letting fxe2x80x2(V) be a differential coefficient of f(V) at the voltage V,
a condition:
f(V1)/{V1xc2x7fxe2x80x2(V1)xe2x88x922f(V1)} greater than f(V2)/{V2xc2x7fxe2x80x2(V2)xe2x88x922f(V2)}xe2x80x83xe2x80x83(2)
The second wiring includes a plurality of second wirings, the pluralities of first and second wirings extend to substantially cross each other, and the pluralities of first and second wirings form a matrix arrangement. Alternatively, the first and second wirings extend substantially parallel to each other. The latter includes so-called ladder-shaped connection.
By applying the voltage V1 to a plurality of electron-emitting devices connected to first wirings while simultaneously selecting a plurality of first wirings, all the devices of the electron source can be pre-driven within a short time. As a result, a multi electron source almost free from variations in characteristics can be realized. Further, more uniform device characteristics can be obtained by combining a driving method of compensating for a voltage drop generated on the first wiring from the second wiring, and in this case, by selecting a proper combination of lines to be simultaneously selected or performing proper calculation of the compensation voltage. A high-quality image display apparatus can be realized using such electron source.
According to the third aspect of the present invention, a method of manufacturing an image forming apparatus having an electron source, and an image forming member for forming an image upon irradiation of electrons emitted by the electron source is characterized in that the electron source manufacturing method of each aspect is used as an electron source manufacturing method.
According to the fourth aspect of the present invention, a manufacturing apparatus for practicing the electron source manufacturing method of each aspect is characterized by comprising first potential application means for applying a potential to the first wiring, second potential application means for applying a potential to each second wiring, and potential determination means for determining the potential applied by the second potential application means.
An example of this electron source manufacturing apparatus is a pre-driving apparatus for a simple matrix of surface-conduction type electron-emitting devices which constitute an electron source by connecting pairs of device electrodes of the devices at intersections of row- and column-direction wirings (second and first wirings), comprising a line selection circuit and power source circuit for selecting a row- or column-direction wiring of a simple matrix and performing pre-driving processing in units of lines in forming devices, a pre-driving current detection circuit for measuring in units of lines a current flowing through the device in pre-driving processing, a control circuit for calculating, on the basis of an output value from the pre-driving current detection circuit, a voltage distribution applied to a column- or row-direction wiring perpendicular to a row- or column-direction wiring connected to the line selection circuit, a voltage distribution generation circuit for generating the voltage distribution calculated by the control circuit, and a driving circuit for driving the column or row of surface-conduction type electron-emitting devices in a simple matrix in accordance with an output from the voltage distribution generation circuit.
This arrangement can solve the problem that the electron-emitting characteristics of electron-emitting devices on a multi electron source substrate vary due to nonuniformity between the devices caused by a voltage drop by the wiring resistance from the feeding terminal to the device terminal. In addition, the device characteristics can be stably maintained. Since pre-driving processing is done in units of lines, the pre-driving processing time can be shortened.
For example, when a row- or column-direction wiring of a simple matrix is selected to perform pre-driving processing in units of lines, a voltage drop generated in the line direction by the wiring resistance can be compensated by the voltage distribution application circuit for generating a voltage distribution on a column or row crossing the row- or column-direction wiring connected to the line selection circuit. At this time, if an output from the voltage distribution application circuit is updated in accordance with the device current which changes upon application of the pre-driving voltage, nonuniformity between the pre-driving voltage values of devices caused by the difference in distance from the feeding terminal can be eliminated.
Accordingly, a multi electron source having many surface-conduction type electron-emitting devices can be uniformly fabricated.
An electron source adjusting method according to the fifth aspect of the present invention has the following steps.
That is, a method of adjusting an electron source having a plurality of electron-emitting devices is characterized by comprising:
the voltage application step of applying potentials to a first wiring commonly connected to a plurality of electron-emitting devices, and a plurality of second wirings respectively connected to the plurality of electron-emitting devices, and applying a voltage V1 to the plurality of electron-emitting devices connected to the first wiring by the potentials applied to the first wiring and the plurality of second wirings, the voltage V1 having a relationship with a maximum value V2 of a voltage applied as a normal driving voltage after the voltage application step, so as to satisfy:
giving a current I flowing upon application of a voltage V when the voltage V falling within a voltage range causing electron emission upon application of the voltage between two electrodes is applied to the device:
I=f(V)xe2x80x83xe2x80x83(1)
and letting fxe2x80x2(V) be a differential coefficient of f(V) at the voltage V,
a condition:
f(V1)/{V1xc2x7fxe2x80x2(V1)xe2x88x922f(V1)} greater than f(V2)/{V2xc2x7fxe2x80x2(V2)xe2x88x922f(V2)}xe2x80x83xe2x80x83(2)
wherein the potential applied to each second wiring is set to reduce a difference in magnitude of the voltage V1 applied to each electron-emitting device as a potential difference between the potential applied to the electron-emitting device through the first wiring and the potential applied to the electron-emitting device through the second wiring.
This adjusting method enables adjusting after shipping, as needed.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.